Polysilicon is a raw material used to produce many products including, for example, semiconductor wafers used for integrated circuits and photovoltaic (i.e., solar) cells. Polysilicon is typically produced by a chemical vapor deposition mechanism in which silicon is deposited from a thermally decomposable silicon compound onto silicon seed particles or granular polysilicon in a fluidized bed reactor. During this deposition process, the temperature in the fluidized bed reactor affects gas density and viscosity, which affect the dynamics of the gas-solid system and resulting reaction kinetics. Therefore, heat is applied to the fluidized bed reactor to increase and maintain an elevated temperature for optimizing the production of polysilicon.
One method of controlling the temperature within the reactor has been to preheat the inlet gases, i.e. silane and the diluting gas, in a controlled manner before they enter the reactor. However, preheating the inlet gases causes premature decomposition of the silane, which results in deposition of silicon in the inlet. Therefore, the temperature within the reactor is generally controlled by heating the reactor walls in industrial applications to prevent the premature decomposition of the silane.
Induction heater systems have been used to elevate the temperature within the fluidized bed reactor by heating the reactor walls. Induction heater systems generally include an electrically conducting work head or coil and a conducting work piece or susceptor located around the reactor walls, inside the coils. An alternating electric current is passed through the coils to create a strong magnetic field around the work piece. The magnetic field produces electric currents, or eddy currents, in the conducting work piece, which generate heat in the work piece though resistive or joule heating. As the alternating electric current passes through the coils, the work piece generates heat and increases the temperature within the reactor walls. However, prior systems for induction heating of fluidized bed reactors have created hotspots within the reactor walls that decrease the lifespan of the fluidized bed reactor.
As a result, there remains a need for induction heater systems and methods that provide better control, e.g., to reduce hot spots within the reactor walls and extend the useful life of reactors.
This Background section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present disclosure, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.